Unless otherwise indicated herein, the materials described in this section are not prior art to the claims in this application and are not admitted to be prior art by inclusion in this section.
A number of scientific methods have been developed in the medical field to detect and/or measure analytes of interest in a person's blood or other bodily fluids. Analytes of interest can include enzymes, reagents, hormones, proteins, cells or other molecules, such as carbohydrates, e.g., glucose. In a typical scenario, a person's blood is drawn and sent to a lab or input into a testing device, where one or more tests are performed to determine the presence or absence of an analyte of interest and/or measure the concentration of the analyte in the blood. However, some analytes are particularly difficult to identify and quantify with conventional sensing techniques. For small or rare analytes, such as circulating tumor cells, for example, only one such cell may be present in 10 mL of blood. Impractically large quantities of blood would have to be drawn or otherwise sampled and analyzed in order to detect such cells or estimate overall concentration in the blood with statistical significance.
Further, these rare or small analytes also present challenges for in vivo testing methods. Rare analytes will infrequently pass within the interrogation field of the detector and, even when they do, they may be difficult to detect. Because the in vivo signal obtained from the analyte of interest is typically weak in comparison to the background, many in vivo analyte detection and characterization techniques can suffer from a low signal-to-noise ratio (SNR). Low SNR can make discerning between target analytes present in the blood, versus other analytes, particles, and tissues, etc. very difficult, especially where the target analytes are rare in the blood or are of a relatively small size. Accordingly, rare analyte testing methods can be much more time consuming (if a large volume of blood must be analyzed), less sensitive, less specific and generally less informative.